Add the crushed tomatoes, diced onion, minced garlic, vegetable broth, chopped basil, oregano, salt, and pepper to the slow cooker.
Stir to combine, then cover and cook on low for 6 hours.
Use an immersion blender to puree the soup directly in the slow cooker until smooth.
Stir in the heavy cream and grated Parmesan cheese until fully combined and the cheese has melted.
Ladle into bowls and top with additional Parmesan if desired.